Papaverine → Pyrrolo(2,1-a)isoquinoline

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A series of novel pyrrolo[2,1-a]isoquinoline dyes was prepared from readily available starting materials via a simple synthetic pathway. One such starting material is papaverine, a naturally occurring alkaloid that is relatively inexpensive and commercially available as its hydrochloride salt. Papaverine hydrochloride was converted to its free base in 97% yield. The free base was subsequently alkylated with phenacyl bromide in refluxing acetone to give 1 in 56% yield (Scheme 1). Refluxing the mixture for one hour produced good results; additional heating resulted in substantial decomposition of 1 to papaverine hydrobromide. Attempts to isolate 1 using benzene as solvent were unsuccessful. Sodium bicarbonate in water was mixed with 1 to give the cyclized product 2 in 82% yield. ##STR15##

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